GF28.60-P-1000VG "Low/High" Shift Mechanism, Function
GF28.60-P-1000VG "Low/High" shift mechanism, function
- with engine 156, 272, 273, 642 [model 164.1]
- with engine 273, 642 [model 164.8]
- Transmission 722.9
- with CODE (430) Offroad package
Function requirements for "Low/High" shift, general
^ Ignition ON
^ Transmission in position "N"
"Low/High" shift, general
The driver can use the Low Range switch (N72s31), which is located in the lower control panel control unit (N72), to switch from the on-road ratio "High" to the off-road ratio "Low".
When the Low Range switch is pressed, the transfer case control unit (N15/7) shifts the gear ratio in relation to:
- Vehicle speed
- Position of transfer case actuator motor (M46/2)
- Additional CAN signals
The transfer case absolute sensor (B57) registers the position of the "High/Low" shift fork in the transfer case and forwards the information to the transfer case control unit.
"Low/High" shift, function sequence
The function sequence is subdivided into the following steps:
^ Function sequence for gear preselection function
^ Function sequence for shifting "High" on-road ratio
^ Function sequence for shifting "Low" low-range gearbox
^ Function sequence for safety concept
Function sequence for gear preselection function
If the driver presses the Low Range switch while the function requirements are not satisfied, the LED in the Low Range switch flashes. When the function requirements are satisfied, the ratio in the transfer case changes. If the Low Range switch is pressed a second time while the preselection function is active, the function is terminated.
During the preselection time period, information and warning messages are displayed in the multifunction display (A1p13) in the instrument cluster (A1) if necessary.
Component Identification:
Function sequence for shifting "High" on-road ratio
The following conditions must be satisfied before the transfer case control unit initiates the ratio change from "Low" to "High":
- Engine speed greater than 400 rpm
- Vehicle speed less than 70 km/h
- Transmission in position "N"
- Vehicle speed while reversing less than 20 km/h
If all the shift conditions are satisfied, the transfer case control unit actuates the transfer case actuator motor and the ratio in the transfer case is changed from "Low" to "High". A red LED integrated in the Low Range switch indicates the current operating state.
When changing the gear ratio from "Low" to "High" the transfer case actuator motor moves the sliding sleeve (3) by the rotation of the motor shaft (8) via the shift fork (7) in the direction of the on road ratio gearing (2). If the sliding sleeve (3) is connected to the on-road ratio gearing (2) of the differential housing (5), then following synchronization the ring gear (6) is fixed via the sliding sleeve (3) and the planetary gears (4) (via the planet gear shaft (1)) in relation to the differential housing (5). The planetary gear set rotates as a unit with a ratio of 1:1.
Component Identification:
Function sequence for shifting "Low" low-range gearbox
The following conditions must be satisfied before the transfer case control unit initiates the ratio change from "High" to "Low":
- Engine speed greater than 400 rpm
- Vehicle speed less than 40 km/h
- Transmission in position "N"
- Vehicle speed while reversing less than 10 km/h
If all the shift conditions are satisfied, the transfer case control unit actuates the transfer case actuator motor and the ratio in the transfer case is changed from "High" to "Low". A red LED integrated in the Low Range switch indicates the current operating state.
When changing the gear ratio from "High" to "Low" the transfer case actuator motor moves the sliding sleeve (3) by the rotation of the motor shaft (8) via the shift fork (7) in the direction of the off road ratio gearing (9). The off-road ratio gearing (9) is fixed in relation to the synchronizer ring (12) and the synchronizer spring (11) on the rear transmission housing (10). After synchronization, the ring gear (6) is connected via the sliding sleeve (3) to the off road ratio gearing (9) and to the rear transmission housing (10). This results in a step-down ratio of 2.93:1.
Function sequence for safety concept
The following safety functions exist to prevent damage in the drive train when shifting from "High" to "Low" (off-road ratio) or from "Low" to "High" (on-road ratio):
- If drive position "D" is engaged during the shift operation, the fully integrated transmission control unit (VGS) (Y3/8n4) is blocked by the transfer case control unit.
- If a shift operation is attempted but fails to mesh (e.g. tooth to tooth), the attempt is repeated. If the shift operation cannot be completed, the ratio previously engaged is retained.
